Filtering of inhaled air is one of the primary functions of the human anterior nasal cavity and upper respiratory tract. The natural filtration mechanism functions as a safeguard against particles being deposited in the lower airways or ultimately in the bronchi.
However, the natural filtration of particles, where especially particles above 10 microns are deposited on the nasal mucosa membrane, can for some individuals be an extreme nuisance, as they develop allergic responses against these particles. In order to protect humans against unwanted particles while breathing, a variety of filters have been developed, a selection of which is described in the following.
For terminology reasons, it should be noted that the vertical central wall of the nose between the left and right nostril is typically called the medial wall or septum of the nose and ends at the low end of the nose, which is called the columella. The nostrils are largely delimited by the septum and the lateral parts, which are the outer wings of the nostrils, bending from the edge of the septum at the tip of the nose to the back edge of the septum near the head skeleton. The forward direction towards the tip of the nose is termed anterior and the back of the nose towards the skull is termed posterior.
Personal air filtering devices can be divided into two main categories: facial masks that cover both mouth and nose and nasal filters that solely cover the nose. Nasal filters can be sub-divided into externally placed nasal filters and internally placed nasal filters.
Many nasal filters have one filter unit for each nostril, the filter units being connected via a U-formed, flexible bridge that clips around the columella of the nose and holds the filter units in place inside the nostrils. The filter units are often elongate with a longitudinal direction and a transverse direction; when inserted into the nose, the longitudinal direction of the filter extends from the anterior part of the nostril at the tip of the nose to the posterior part of the nostril near the skull, and the transverse direction extends from the septum of the nose to the lateral part of the nose.
Existing internally placed nasal filters can be categorized broadly into cone-like devices and flat filter devices. The advantages of the former are argued to be flexibility, steady positioning, larger surface areas for filtration and level of comfort, for example as disclosed in US patent or patent applications U.S. Pat. Nos. 2,055,855, 7,748,383, US2007/0193233 and US2005/0205095. The advantages of the latter are argued to be minimal visibility, invasiveness, and increased comfort of use.
Substantially flat filter type devices are disclosed in Canadian patent application CA26589940, British patent application GB2289846, German patent laid open document DE3914606A1, Japanese patent application JP2002-345986A, German utility model DE202010001203U1, US patents and applications U.S. Pat. No. 2,046,664, US228268, U.S. Pat. Nos. 5,392,773, 7,156,099, US2007/0283963, US2008/0087286, US2012/0111334, and International patent applications WO2005/120645, WO2009/097553, and WO2011/041921.
In order for an internal nasal filter to work well, be acceptable and attractive to the user in daily life, it must fulfil some basic objectives: It must be near to invisible, it must allow adequate air movement without a steep increase in resistance while breathing, it most remove what it is claiming to remove, it must be able to accommodate a variety of nasal sizes and shapes, it must substantially follow the curvature of the nasal cavity so that all inhaled air passes through the filtration mechanism, and finally it must be comfortable to wear.
The primary drawback of cone-like structures is generally the sheer mass of material that has to be placed in the nasal cavity. This increases visibility of the filter; lowers the available space for airflow, thus, increasing resistance; and feels uncomfortable for users, thus, lowering compliance.
The primary drawbacks of flat nasal filters are generally their lack of flexibility and adaptability, their tendencies to wobble during nasal movement and breathing, which leaves loopholes for the inhaled air and their transverse position in the cavity that results in pain, especially when touching the nose.
Both cone-like nasal filters and flat filters have been made in one and two or more component solutions where the basic argument for introducing more components has been the idea of having exchangeable parts. The most basic drawback of these systems is the increased resistance to airflow that occurs because the material takes up too much space in the nasal cavity.
All of the above mentioned general drawbacks have resulted in lower adaptability among potential users than what would be expected if all of the basic objectives were reached.
European Patent EP2089115B1 describes an internal nasal filter comprising lunette-shaped filtering components on an oval support that is connected to a flexible U-shaped bridge that functions as a clip around the lower edge of the cartilage of the nose. The ends of the flexible U-shaped element (from hereon referred to as shanks) are placed substantially perpendicular to the flexible U-shaped element. This results in the shanks and the filter being perpendicular to the air stream, which makes sense from a filtration perspective. However, it also results in increased resistance as the shanks are placed in the primary air stream thus resulting in laboured breathing. Furthermore the angle at which the shanks are placed and their solidity results in discomfort when touching or moving the nose. Although, EP2089115B1 utilises the idea of using the more flexible filtering components to adjust for different nose sizes and variations, the embodiments of its shanks lack the ability to uphold a filtering component without internal stiffness. This results in discomfort because of the necessary stiff structural characteristics of the filtering components and their perpendicular angle to the nasal canal. It also results in gaps along the curvature of the nasal cavity through which unfiltered air is inhaled.
It is therefore desirable to provide improvements in the art.